Spherical gradient for spot light
I think you want to make something like fake IES lights. I don't know how to make it with spotlights, but maybe this will help you. So here we go!

Final result:



Steps:


Create simple Circle filled with Ngon or Triangle, or even fill it as you pleased and scale it down to 0.1.
Create this node setup (I'll explain it later):




Most interesting stuff:

Light Falloff.
You can control here light strength and smoothness.

Color Ramp.
This will make gradients as you like. Try adding/deleting/shifting colors and you'll see the magic.

Blackbody.
Real deal here. It's simulating temperature of light. You can delete it and set any color you want.

That's it. You have now fancy fake IES lights with color temperature.

Blend file: